/*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project licenses this file to you under the Apache License,
    * version 2.0 (the "License"); you may not use this file except in compliance
    * with the License. You may obtain a copy of the License at:
    *
    *   https://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations
   * under the License.
   */
  package io.netty5.example.portunification;
  
  import io.netty5.buffer.api.Buffer;
  import io.netty5.channel.ChannelHandlerContext;
  import io.netty5.channel.ChannelPipeline;
  import io.netty5.example.factorial.BigIntegerDecoder;
  import io.netty5.example.factorial.FactorialServerHandler;
  import io.netty5.example.factorial.NumberEncoder;
  import io.netty5.example.http.snoop.HttpSnoopServerHandler;
  import io.netty5.handler.codec.ByteToMessageDecoder;
  import io.netty5.handler.codec.compression.ZlibCodecFactory;
  import io.netty5.handler.codec.compression.ZlibWrapper;
  import io.netty5.handler.codec.http.HttpContentCompressor;
  import io.netty5.handler.codec.http.HttpRequestDecoder;
  import io.netty5.handler.codec.http.HttpResponseEncoder;
  import io.netty5.handler.ssl.SslContext;
  import io.netty5.handler.ssl.SslHandler;
  
  /**
   * Manipulates the current pipeline dynamically to switch protocols or enable
   * SSL or GZIP.
   */
  public class PortUnificationServerHandler extends ByteToMessageDecoder {
  
      private final SslContext sslCtx;
      private final boolean detectSsl;
      private final boolean detectGzip;
  
      public PortUnificationServerHandler(SslContext sslCtx) {
          this(sslCtx, true, true);
      }
  
      private PortUnificationServerHandler(SslContext sslCtx, boolean detectSsl, boolean detectGzip) {
          this.sslCtx = sslCtx;
          this.detectSsl = detectSsl;
          this.detectGzip = detectGzip;
      }
  
      @Override
      protected void decode(ChannelHandlerContext ctx, Buffer in) throws Exception {
          // Will use the first five bytes to detect a protocol.
          if (in.readableBytes() < 5) {
              return;
          }
  
          if (isSsl(in)) {
              enableSsl(ctx);
          } else {
              final int magic1 = in.getUnsignedByte(in.readerOffset());
              final int magic2 = in.getUnsignedByte(in.readerOffset() + 1);
              if (isGzip(magic1, magic2)) {
                  enableGzip(ctx);
              } else if (isHttp(magic1, magic2)) {
                  switchToHttp(ctx);
              } else if (isFactorial(magic1)) {
                  switchToFactorial(ctx);
              } else {
                  // Unknown protocol; discard everything and close the connection.
                  in.resetOffsets();
                  ctx.close();
              }
          }
      }
  
      private boolean isSsl(Buffer buf) {
          if (detectSsl) {
              return SslHandler.isEncrypted(buf);
          }
          return false;
      }
  
      private boolean isGzip(int magic1, int magic2) {
          if (detectGzip) {
              return magic1 == 31 && magic2 == 139;
          }
          return false;
      }
  
      private static boolean isHttp(int magic1, int magic2) {
          return
              magic1 == 'G' && magic2 == 'E' || // GET
              magic1 == 'P' && magic2 == 'O' || // POST
              magic1 == 'P' && magic2 == 'U' || // PUT
              magic1 == 'H' && magic2 == 'E' || // HEAD
             magic1 == 'O' && magic2 == 'P' || // OPTIONS
             magic1 == 'P' && magic2 == 'A' || // PATCH
             magic1 == 'D' && magic2 == 'E' || // DELETE
             magic1 == 'T' && magic2 == 'R' || // TRACE
             magic1 == 'C' && magic2 == 'O';   // CONNECT
     }
 
     private static boolean isFactorial(int magic1) {
         return magic1 == 'F';
     }
 
     private void enableSsl(ChannelHandlerContext ctx) {
         ChannelPipeline p = ctx.pipeline();
         p.addLast("ssl", sslCtx.newHandler(ctx.bufferAllocator()));
         p.addLast("unificationA", new PortUnificationServerHandler(sslCtx, false, detectGzip));
         p.remove(this);
     }
 
     private void enableGzip(ChannelHandlerContext ctx) {
         ChannelPipeline p = ctx.pipeline();
         p.addLast("gzipdeflater", ZlibCodecFactory.newZlibEncoder(ZlibWrapper.GZIP));
         p.addLast("gzipinflater", ZlibCodecFactory.newZlibDecoder(ZlibWrapper.GZIP));
         p.addLast("unificationB", new PortUnificationServerHandler(sslCtx, detectSsl, false));
         p.remove(this);
     }
 
     private void switchToHttp(ChannelHandlerContext ctx) {
         ChannelPipeline p = ctx.pipeline();
         p.addLast("decoder", new HttpRequestDecoder());
         p.addLast("encoder", new HttpResponseEncoder());
         p.addLast("deflater", new HttpContentCompressor());
         p.addLast("handler", new HttpSnoopServerHandler());
         p.remove(this);
     }
 
     private void switchToFactorial(ChannelHandlerContext ctx) {
         ChannelPipeline p = ctx.pipeline();
         p.addLast("decoder", new BigIntegerDecoder());
         p.addLast("encoder", new NumberEncoder());
         p.addLast("handler", new FactorialServerHandler());
         p.remove(this);
     }
 }